Phosphor and treatment method for the same

ABSTRACT

The present invention aims at realizing a PDP and a mercury-free fluorescent lamp feasible to maintain excellent luminescent characteristics over long periods by suppressing time-lapse changes in luminescent characteristics of a phosphor that is excited by vacuum ultraviolet light to thereby emit light. To accomplish this object, the oxide phosphor of the invention comprises individual particles, each of which has a region at and near the surface thereof modified, and the elemental composition of the surface region is in a more oxidized state than that of the internal region of the particles. Alternatively, the surface region has more halogen or chalcogen in the elemental composition. In the phosphor treatment method of the invention, the surface region of individual phosphor particles is selectively modified by (i) forming a highly reactive gas atmosphere by exciting gas which contains reactive gas, and (ii) exposing the phosphor to the gas atmosphere.

TECHNICAL FIELD

The present invention relates to phosphors used for light-emittingelements, in particular to phosphors capable of being excited by vacuumultraviolet light and used for plasma display panels (PDP) andmercury-free fluorescent lamps.

BACKGROUND ART

An AC-driven surface discharge PDP having a three-electrode structure isknown as a PDP suitable for a full color display using three colorphosphors.

FIG. 9 is a schematic cross-sectional diagram showing a structure of acommon AC-driven surface discharge PDP.

The PDP shown in the drawing comprises a front glass substrate 1 and arear glass substrate 5, which are disposed parallel to one another.Formed on the front glass substrate 1 are display electrodes 2 that arecovered by a dielectric glass layer 3 and a magnesium oxide (Mgo)dielectric protective layer 4 (see, for example, Patent Reference 1).

On the rear glass substrate 5, on the other hand, address electrodes 6and barrier ribs 7 are disposed, and phosphor layers 9-11 of respectivecolors (red, green, and blue), which are composed of oxide phosphors,are each provided in the space between two adjacent barrier ribs 7.

The front glass substrate 1 as formed above is disposed on the barrierribs 7 arranged on the rear glass substrate 5, and discharge gas isfilled between these substrates 1 and 5 to form a discharge space 8.

In this PDP, vacuum ultraviolet light (predominantly, a wavelength of147 nm) is generated through an electric discharge, and the phosphorlayers 9-11 of three colors are excited to thereby emit light, whichresults in a display in colors.

The above PDP can be manufactured as follows.

A silver paste is applied to the front glass substrate 1, and then firedto form the display electrodes 2. Further, a dielectric glass paste isapplied over the display electrodes 2, and then fired to form adielectric glass layer 3, on which a protective layer 4 is formed.

Onto the rear glass substrate 5, on the other hand, a silver paste isapplied and fired to form the address electrodes 6. Next, a glass pasteis applied at predetermined intervals, and then fired to form thebarrier ribs 7. Subsequently, the phosphor layers 9-11 are formed byrespectively applying phosphor pastes of individual colors to the spacesbetween the barrier ribs 7, and firing the phosphor pastes at around500° C. to remove resin components and the like therefrom. After thisfiring process for forming the phosphor layers 9-11, sealing glass fritsare applied around the edge of the rear glass substrate 5 to herewithform a sealing glass layer, and calcinated at around 350° C. in order toremove resin components and such from the formed sealing glass layer(frit calcination process).

Then, the front glass substrate 1 and the rear glass substrate 5 arelaid on top of each other so that the display electrodes 2 and theaddress electrodes 6 face at right angles to one another. Thesesuperimposed glass substrates are attached and sealed by heating at atemperature (approximately 450° C.) higher than the softeningtemperature of the sealing glass (sealing process).

Subsequently, as the sealed panel formed of the front and rear glasssubstrates 1 and 5 is heated up to around 350° C., air is evacuated fromthe internal space formed between the both glass substrates, i.e. thespace which is formed between the front and rear glass substrates 1 and5, and to which the phosphor layers are exposed (evacuation process)After the evacuation process is completed, discharge gas is introducedto the space until the pressure reaches a predetermined point (normally,39.9 kPa-66.5 kPa, or 300 Torr-500 Torr).

With such a PDP, there has been a challenge to improve the luminescentcharacteristics, including the luminance, for example, and to reducetime-lapse changes in luminescent characteristics of the phosphor layersso as to realize an extended quality assurance period.

As to a PDP, in particular, it is sometimes the case that the qualityassurance period is determined based on the time-lapse changes inluminescent characteristics of the phosphors used for a luminous displayunit of the PDP.

Due, for example, to moisture and application of heat in the PDPmanufacturing process, the luminance of phosphors deteriorates and thechromaticity of the phosphors also changes. Thus, the time-lapse changesin phosphors during the PDP manufacturing process leads to degradationof the panel's characteristics. In addition, the phosphor layers areexposed to plasma associated with an electric discharge during the timewhen the PDP is in operation, which results in further changes inphosphor layers over time. Furthermore, the time-lapse changes inphosphors sometimes lead to deterioration in the PDP's luminescentcharacteristics over time, which in turn results in the end of theproduct's life.

This is also the case with a mercury-free fluorescent lamp of which thephosphor layer is excited by vacuum ultraviolet light to emit light. Thetime-lapse changes in phosphor layer may account for the duration oflife.

Under such a circumstance, with light-emitting elements such as a PDPand a mercury-free fluorescent lamp, it is desired to suppress thetime-lapse changes in luminescent characteristics of the phosphorscaused during the manufacturing process and the time when theselight-emitting elements are in operation.

As a technology for suppressing the time-lapse changes in phosphors, amethod in which the phosphors are heat-treated (i.e. fired) at a hightemperature of approximately 1100° C. to improve the crystallinity iswell known.

In addition, in order to suppress deterioration in the phosphor layers,there is a known method in which the surface of phosphor particles iscovered with a protective coat made of MgO by using vapor deposition,dipping, sputtering, or spraying techniques as described in PatentReference 1.

As a method of forming a long lasting phosphor, Patent Reference 2proposes to supply a coating precursor, e.g. trimethyl aluminum, andmixed gas composed of oxygen and ozone into a reactor vessel, and coatphosphor particles by spending a considerable amount of time.

-   -   Patent Reference 1: Japanese Laid-Open Patent Application        Publication No. H8-31325    -   Patent Reference 2: Japanese Laid-Open Patent Application        Publication No. 2000-96044

DISCLOSURE OF THE INVENTION

To cover individual phosphor particles with a protective coat, such asMgO, requires a device like a vacuum evaporator, as in Patent Reference1 above, which carries an additional cost.

According to the method described in Patent Reference 2, it takes a longtime period of 40 to 70 hours to coat the phosphor particles. Inaddition, when the phosphor particles are processed at a hightemperature, the luminescent characteristics tend to degrade althoughthe time-lapse changes of the characteristics are reduced.

The present invention aims at realizing a PDP and a mercury-freefluorescent lamp feasible to maintain excellent luminescentcharacteristics over a long period of time by suppressing the time-lapsechanges in luminescent characteristics of a phosphor which is excited byvacuum ultraviolet light to thereby emit light.

In order to accomplish the above object, an oxide phosphor of thepresent invention is in particulate form, wherein each particle has asurface region including a vicinity thereof modified so that anelemental composition of the surface region is in a more oxidized statethan an elemental composition of an internal region of the particle.

Here, the “surface” means an external surface where no protective layerand the like are formed.

The “surface region including a vicinity” denotes a region within theindividual phosphor particles that constitute a phosphor excited byvacuum ultraviolet light, and this region is up to tens of nanometersdeep from the surface.

Alternatively, in the oxide phosphor of the present invention, eachparticle has a surface region including a vicinity thereof modified sothat an elemental composition of the surface region includes morehalogen or chalcogen than an elemental composition of an internal regionof the particle. Here, it is preferable that halogen atoms or chalcogenatoms are chemically bound to the surface region.

The phosphor treatment method of the present invention comprises a stepof: selectively modifying a surface region, including a vicinitythereof, of individual phosphor particles that constitute a phosphor by(i) forming a highly reactive gas atmosphere by exciting gas thatcontains reactive gas, and (ii) exposing the phosphor to the gasatmosphere.

Here, the “reactive gas” is, for example, oxygen, gas composed ofhalide, or gas composed of chalcogen compounds.

The “surface region including a vicinity” of individual phosphorparticles denotes a region over which vacuum ultraviolet lightpenetrates from the surface of the phosphor particles (tens ofnanometers deep from the surface), and a region deeper than this regionis referred to as an internal region.

The “highly reactive gas atmosphere” means a gas atmosphere in a phasethat is chemically more reactive to the surface of the phosphor ascompared to the original gas form. This is, for example, an excitedstate containing radicals and ions therein. When oxygen (original gasform) is used as the reactive gas, the highly reactive gas atmosphere isa phase of gas containing radical oxygen or ozone, both of which exhibitstrong oxidizing properties.

“Selectively modifying a surface region including a vicinity ofindividual phosphor particles that constitute a phosphor” means that thesurface region including the vicinity is modified so that a degree ofmodification thereof be greater than in the internal region of theparticles.

The present invention described above allows to suppress the time-lapsechanges in luminescent characteristics, and the reason for this isthought to be as follows.

With an oxide phosphor, elements included in the composition aregenerally the same to the entire particle. It is considered thatluminescent characteristics of the phosphor, however, change over timedue to the following factors:

-   -   i) moisture adsorption to the surface of the phosphor;    -   ii) defects in the phosphor crystal structure;    -   iii) substances other than the phosphor crystals mixed in;    -   iv) change in crystal structure due to heat application to the        phosphor; and    -   v) destruction of the crystal structure caused by exposing the        phosphor to plasma associated with an electric discharge.

Against these factors, the present invention described above fillsoxygen vacancies in the vicinity-included surface region of theparticles of the oxide phosphor, and thereby improves the crystallinityof the phosphor. As a result, the time-lapse changes in luminescentcharacteristics mainly arisen, among the factors above, from the factorii (defects in the phosphor crystal structure) can be suppressed.

The occurrence of the factors i and iv (moisture adsorption to thephosphor, and change in crystal structure) is often attributable to thedefects in the phosphor crystal structure. With the present invention,however, since the phosphor crystal defects are compensated and therebycrystallinity is improved, the changes over time due to the factors iand iv can be suppressed.

Here, the vicinity-included surface region is selectively modified, andtherefore the modification treatment can be processed over a shortperiod of time as compared to the case where the internal region is alsomodified. As a result, this leads to cost savings, and would reduce thedamage which is caused to the phosphor in association with themodification treatment.

A wide variety of gases can be used as introduced gas. By selectingtypes of gases for use, a specific degradation factor can be eliminated,and furthermore several degradation factors together can be eliminatedat once.

In addition, according to the treatment method of the present invention,the modification of the phosphor is realized simply by exposing thephosphor to the introduced gas. Thus, the treatment process iscomparatively simple, and does not require an expensive device such as avacuum evaporator.

It is preferable to use a mixture of reactive gas and either rare gas orinert gas as the introduced gas since this facilitates a formation ofthe highly reactive gas atmosphere as well as reduces damage caused tothe phosphor.

If fluorine forms bonds with the preprocessed phosphor components in thevicinity-included surface region of the phosphor particles, a layer thatfunctions as a protective layer having water repellency is formed nearthe surface of the phosphor, and thereby the time-lapse changes of thephosphor are further suppressed.

In the case when the phosphor is an alkaline earth metal aluminatephosphor, fluorine can be present, being bound with the alkaline earthmetal.

In order to contain fluorine in the vicinity-included surface region ofphosphor particles, for example, first fluorinated gas is included inthe introduced gas. Then, the introduced gas with the fluorinated gas isexcited, and the phosphor is exposed to the excited gas atmosphere.

When a phosphor layer used for a light-emitting element is composed ofsuch an oxide phosphor of the present invention, the phosphor layer alsoobtains reduced time-lapse degradation of luminescent characteristics.

Here, within each of the phosphor layers, the oxide phosphor of thepresent invention described above may be disproportionally distributed,with more at and near a surface thereof than in an inner region. In thiscase also, the characteristics at and near the surface of the phosphorlayer are maintained, which results in suppressing the time-lapsedegradation of the luminescent characteristics.

Such a light-emitting element can be manufactured by a method comprisinga step of: modifying, within each of one or more phosphor layers formedon a substrate, a region at and near a surface thereof by (i) forming ahighly reactive gas atmosphere by exciting gas that contains reactivegas, and (ii) exposing the substrate to the gas atmosphere.

In particular, the use of the oxide phosphor of the present invention inphosphor layers of a PDP and a mercury-free fluorescent lamp has abeneficial effect on suppressing the time-lapse degradation of theluminescent characteristics of these light-emitting elements.

A phosphor used for a PDP and a mercury-free fluorescent lamp has anexcitation wavelength of mainly 147 nm, which is in the range of thevacuum ultraviolet. Therefore, the vacuum ultraviolet light is absorbedin the vicinity-included surface region of the phosphor particles, andconverted to visible light within the region. Accordingly, if theluminescent characteristics of the vicinity-included surface region ofthe phosphor particles are maintained, the luminescent characteristicsof the PDP and mercury-free fluorescent lamp can also be maintained.

Among oxide phosphors, ones that include, in their elementalcompositions, a luminescent center metal (e.g. Eu and Mn) possible tohave a plurality of valence states generally have excellent luminescentcharacteristics. Europium-activated oxide phosphors, in particulareuropium-activated alkaline earth metal aluminate phosphors, exhibithigh luminous efficiency in the vacuum ultraviolet range. However, thesephosphors are susceptible to the time-lapse changes in luminescentcharacteristics.

Therefore, applying the present invention to this type of oxide phosphoryields a significant effect.

With this type of oxide phosphor, the time-lapse changes in luminescentcharacteristics can be suppressed by selectively modifying thevicinity-included surface region of the phosphor particles by making theluminescent center metal in the vicinity-included surface region have ahigher average valence as compared to the internal region of theparticles.

An oxide phosphor described as Ba_(1-x)Sr_(y)Eu_(z)MgAl₁₀O₁₇, where0.05≦x≦0.40, 0≦y≦0.25, 0.05≦z≦0.30, and x−y≦z, in particular, exhibitshigh luminous efficiency in the vacuum ultraviolet range, and iscommonly used for PDPs and mercury-free fluorescent lamps. However, suchan oxide phosphor is susceptible to the time-lapse changes inluminescent characteristics, and therefore an application of the presentinvention to the oxide phosphor yields a significant effect. Here, whenthe europium concentration in the vicinity-included surface region ofthe phosphor particles is z′, it is desirable that (1) a relation in theform of z≦z′≦5z be satisfied, (2) within each of the phosphor particleoverall, a proportion of divalent europium to the total amount ofeuropium be no less than 60% but no more than 95%, and (3) in thevicinity-included surface region within each of the particles, theproportion of divalent europium be no less than 5% but no more than 30%,and more preferably no less than 10% but no more than 20%.

It is preferable to implement the phosphor treatment method of thepresent invention in the following manner.

In order to form the highly reactive gas atmosphere, gas containingreactive gas is excited, and a gas atmosphere in a plasma state isthereby formed. Herewith, the reactive gas is continuously maintained inan excited state, and thereby it is expected to achieve an excellentmodification effect.

If the highly reactive gas atmosphere is formed at or close toatmospheric pressure, there is no need for depressurizing the gasatmosphere, which results in a high throughput of the treatment process.As a result, this has an advantage in processing time reduction as wellas cost savings.

The introduced gas may be brought into a certain reactive state byapplying energy in order to form the highly reactive gas atmosphere.

In this case, when a location at which the energy is applied to theintroduced gas is separated from a location at which the processingphosphor is exposed to the highly reactive gas atmosphere, the phosphoris free from damage.

For instance, the gas atmosphere may be formed outside a treatmentvessel by (i) introducing the gas containing the reactive gas into thetreatment vessel, (ii) applying energy to excite the introduced gas, and(iii) ejecting the excited gas therefrom.

Concrete methods for applying energy to the introduced gas include anapplication of ultraviolet light. This method allows to form the highlyreactive gas even at a low temperature.

It is desirable that the ultraviolet light is applied to the gascontaining the reactive gas without illuminating the surface of thephosphor.

As another concrete method for applying energy to the introduced gas, ahigh-frequency voltage is applied to the introduced gas so as toelectrically discharge and thereby become excited.

When the phosphor is exposed to the highly reactive gas atmosphere, thereaction between the phosphor and the reactive gas will be acceleratedif the phosphor is in a heated state. Note however that the heatingtemperature is preferably 300° C. or lower, and more preferably 100° C.or lower.

In the case that the introduced gas includes molecular oxygen, ozone ormonatomic oxygen is formed by exciting the introduced gas. Herewith,crystal defects at and near the surface of phosphor crystals can becompensated, and thereby crystallinity of this region is improved. As aresult, degradation factors due to crystal defects can be eliminated,and a phosphor having smaller time-lapse changes can be realized.

When a plurality of kinds of phosphors is impregnated with the formedreactive atmosphere, the phosphors may be processed by altering thetreatment method for each kind of the phosphors. Degradation factors ofphosphors are not uniform, and differ for each kind. Therefore, atreatment appropriate to cope with degradation factors of each phosphorcan be conducted by altering treatment parameters, such as types of theintroduced gas and the like.

It is often the case that several different types of phosphors are usedin a luminaire and an image display device, for example. Here, when itis sought to maintain the luminescent characteristics of these devices,i.e. to maintain a balance of all colors over long period, it isdesirable to conduct appropriate treatments for degradation factors ofrespective phosphors by altering the treatment method for each kind ofphosphor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a structure of a phosphor treatment apparatus used inthe first embodiment for processing a phosphor;

FIG. 2 includes an enlarged view of a phosphor layer 23 on theprocessing object 22 and a diagrammatic view illustrating a structure ofphosphor particles 100 that constitute the phosphor layer 23;

FIG. 3 illustrates an example of how to carry out a modificationtreatment on phosphor layers of respective colors on a substrate;

FIG. 4 is a characteristic graph showing measurements of chromaticity yprior to and after a deterioration test obtained through an experimentwhere the modification treatment was performed on phosphors by changingthe number of treatments;

FIG. 5 shows a structure of a phosphor treatment apparatus used in thesecond embodiment;

FIG. 6 is a characteristic graph showing measurements of changes inchromaticity y obtained through an experiment where the modificationtreatment was performed on phosphors by changing the temperature forheating a substrate before the deterioration test was carried out;

FIG. 7 is a characteristic graph showing measurements of luminescenceintensity obtained through an experiment where the modificationtreatment was performed on phosphors by changing the temperature forheating the substrate;

FIG. 8 illustrates a structure of a phosphor treatment apparatus used ina third embodiment; and

FIG. 9 is a schematic cross-sectional diagram illustrating a structureof a common AC surface discharge PDP.

BEST MODE FOR CARRYING OUT THE INVENTION

The following gives an account of preferred embodiments of the presentinvention in reference to drawings.

1. First Embodiment

In a first embodiment, source gas is introduced, and a high-frequencyvoltage is applied to the source gas to electrically discharge andthereby become excited. Due to this excitation, an atmosphere ofactivated gas having high reactivity is formed. Then, a phosphorcomposed of phosphor particles is exposed to the reactive atmosphere soas to modify a surface region of the individual phosphor particlesincluding the vicinity.

Here, the source gas includes reactive gas that, when raised to anexcited state, becomes highly reactive to the phosphor particles.Oxygen, halogen, gas composed of halide, and gas composed of chalcogencompounds are specific examples of such reactive gas.

1.1 Phosphor Treatment Apparatus

FIG. 1 illustrates a structure of a phosphor treatment apparatus usedfor processing a phosphor in the first embodiment.

As shown in FIG. 1, in the phosphor treatment apparatus, a reactorvessel 17, in which source gas 14 is excited, is placed between an earthelectrode 15 and a high-voltage electrode 16, and a mobile stage 24 forconveying a processing object 22 is disposed in the vicinity of thereactor vessel 17.

The processing object 22 is composed by applying an oxide phosphor ontoa substrate 22 a to form phosphor layers 23. The processing object 22 ismade by mixing, e.g., BaMgAl₁₀O₁₇:Eu²⁺ (BAM), which is a blue phosphor,with a binder, and then applying the mixed substance onto the substrate22 a made of quartz.

A high-frequency power source 21 is connected to the high-voltageelectrode 16.

The reactor vessel 17 that is made of a dielectric material is insulatedfrom the earth electrode 15 and the high-voltage electrode 16. Providedin the reactor vessel 17 are a gas inlet 18 used for introducing thesource gas 14 including reactive gas, and a gas outlet 19 used fordischarging excited gas. Here, a quartz tube is used as the reactorvessel 17.

By driving the high-frequency power source 21, a high frequency electricfield is applied to gas introduced into the reactor vessel 17.

It is preferable to use a mixture of reactive gas and either rare gas orinert gas as the source gas 14, although the reactive gas by itself maybe used.

Note here that included as members of the rare gas family are helium(He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn),while the inert gas group includes nitrogen (N₂) in addition to theabove members of the rare gas family.

If included in the introduced source gas, rare gas contributes to theoccurrence of an electric discharge in the reactor vessel 17. Ifreactive gas by itself is used as the source gas 14, a phosphor beingprocessed is susceptible to damage caused by plasma exposure. Therefore,it is preferable to mix inert gas with reactive gas and use the mixtureas the source gas 14, which allows to mitigate the plasma damage causedto the phosphor.

Although the inside of the reactor vessel 17 may be either pressurizedor depressurized, the modification treatment can also be conducted at orclose to atmospheric pressure with using neither a pressure device nor adecompression device. The pressure range of the reactor vessel 17 insideis preferably in the range of 1 kPa to 10 Mpa, and more preferably 10kPa to 110 kPa.

The mobile stage 24 is able to convey the processing object 22 in anydirection along a main plane of the substrate 22 a so that the outlet 19scans the surface of the processing object 22.

1.2 Phosphor Treatment Method and Advantageous Effects

A treatment method for processing the processing object 22 with the useof the above phosphor treatment apparatus is described here.

At the same time when the source gas 14 is introduced into the reactorvessel 17 from the inlet 18, the high-frequency power source 21 isdriven.

The processing object 22 is placed on the stage 24, and conveyed in sucha manner that the outlet 19 scans the surface of the processing object22.

Herewith, as the source gas 14 goes through the inside of the reactorvessel 17, energy is given to the gas, that is, a high frequencyelectric field is applied to the gas. The source gas 14 is therebyexcited and activated, and then this activated gas is flown out from theoutlet 19. In FIG. 1, a symbol with a reference number of 20 attacheddenotes the activated gas. Subsequently, the phosphor layers 23 areexposed to the activated gas 20. Since having been brought to a reactivestate, the activated gas 20 comes in contact with the surface ofindividual phosphor particles that constitute the phosphor layer 23, andreacts with the surface region (including the vicinity) withinindividual particles. Parts where crystal defects have been formed, inparticular, readily react with the activated gas 20, and thecrystallinity of the vicinity-included surface region of the phosphorparticles will be improved by this reaction. The region in theindividual phosphor particles is impregnated with the activated gas 20.

FIG. 1 provides an example in which mixed gas composed of: oxygen as thereactive gas; He as the rare gas, which contributes to an electricdischarge; and Ar as the inert gas, is used as the source gas 14 to beintroduced into the reactor vessel 17, which mitigates plasma damage.

FIG. 2 includes an enlarged view of one phosphor layer 23 formed on theprocessing object 22 and a diagrammatic view illustrating a structure ofprocessed phosphor particles 100 that constitute the phosphor layer 23.

As shown in FIG. 2, the phosphor layer 23 includes a large number ofphosphor particles 100. The activated gas 20 includes activated oxygen(O) in addition to the elements (He, Ar, and O₂) composing the sourcegas 14.

The activated gas 20 reacts with the parts having crystal defects in thevicinity-included surface region. At this point, if carbon atoms arepresent in the vicinity-included surface region of the phosphorparticles 100, the activated oxygen atoms (O) and ozone (O₃) arecombined with the carbon atoms to form carbon dioxide and such through aradical reaction, for instance. As a result, carbon is excluded from thesurface of the phosphor particles 100 and the surrounding.

Consequently, the processed phosphor particles have fewer crystaldefects in the vicinity-included surface region, which results insuppressing the time-lapse degradation of the luminescentcharacteristics.

If impurities produced when the phosphor was synthesized or impuritiescaught up during a process of forming the phosphor layers are present inthe vicinity-included surface region of the phosphor particles, theimpurities may trigger accelerating the time-lapse changes in phosphor.Here, however, when the activated gas 20 contacts the phosphorparticles, the impurities react with the activated gas 20, and thereforethe effect of eliminating these impurities is also anticipated.

The source gas 14 may contain gas including fluorine (fluorinated gas)as the reactive gas. In this case, it is preferable to set thefluorinated gas in the range of 0.1% to 10% of the volume of the sourcegas 14.

In this particular case, another effect can be obtained in addition tothe effect described above. Here, fluorine compounds are formed in amodified portion 102, and a water repellent layer is formed on thesurface of the phosphor particles due to the fluorine compounds. As aresult, the amount of moisture adsorbed to the phosphor is reduced,which in turn suppresses the time-lapse changes in the phosphor.

Note that in the case where the vapor pressure of the source gas 14 islow at ambient temperatures, the source gas 14 may be heated so as tohave a high vapor pressure before being introduced into the reactorvessel 17. Here, the temperature for heating the introduced gas ispreferably in the range of 50 to 600° C.

In order to accelerate the reaction of the activated gas 20 with thephosphor 23, a heating medium, for example, may be installed to thestage 24 so that the phosphor layer 23 will be heated in the range of100 to 300° C. before, during, or after the phosphor layer 23 beingexposed to the activated gas 20.

Alternatively, a mechanism for voltage application, for example, may beprovided in the stage 24. By using this mechanism at a time when thephosphor layer 23 is exposed to the activated gas 20, the phosphor layer23 is brought to be positively or negatively charged so that ions in theactivated gas 20 are drawn to the phosphor layer 23. With thismechanism, the reaction between the activated gas 20 and the phosphor 23can also be accelerated.

1.3 Structure of Modified Phosphor Particles and Advantageous Effects

Each of the phosphor particles 100 processed as described above has anunmodified portion 101 in the internal region of the particle, and amodified portion 102 in the vicinity-included surface region of theparticle. The modified portion 102 is a portion which has been modifiedby the activated gas 20, while the unmodified portion 101 has not beenmodified by the gas.

In the case when oxygen is used as the reactive gas in the phosphormodification treatment, although elements constituting the modifiedportion 102 are identical with those constituting the unmodified portion101, the modified portion 102 has a more oxidized form of elementalcomposition as compared to the unmodified portion 101. Alternatively,when halogen, gas composed of halide, or gas composed of chalcogencompounds is used as the reactive gas, elements of these will becontained in the modified portion 102.

As described above, the modified portion 102 has fewer crystal defectswhen compared to the corresponding portion of unprocessed particles, andthe crystallinity has been improved.

Therefore, the use of the processed phosphor particles 100 in thephosphor layers of display devices and lamps achieves an effect ofsuppressing the time-lapse changes in phosphor layers. This effect isespecially fully realized in a PDP and a mercury-free fluorescent lamp,of which phosphor layers are excited by vacuum ultraviolet light tothereby emit light, because, in these devices, only thevicinity-included surface region of the phosphor particles contributesto the emission.

The following describes considerations related to a thickness d of themodified portion 102.

The thickness d of the modified portion 102 (i.e. a depth of themodified portion 102 from the surface of the particle) is adjustable bychanging the length of time to expose the phosphor particles 100 to theactivated gas 20. The thickness d becomes larger as the phosphorparticles 100 are exposed to the gas for a longer time.

Used for a PDP is a phosphor excited mainly by vacuum ultraviolet light.In such a phosphor, a region to be excited to emit light is, within theindividual phosphor particles, up to tens of nanometers deep from thesurface. Note however that the depth of this excitation-emission regionchanges over time to some extent. Consequently, in order to suppress thetime-lapse changes in luminescent characteristics of the phosphor, it isdesirable that the thickness d of the modified portion 102 in thephosphor particles 100 be set sufficiently large, being more than thedepth of the excitation-emission region.

On the other hand, in order to make the thickness d of the modifiedportion 102 large, the phosphor particles 100 need to be exposed to theactivated gas 20 over an extended time period. As a result, the largerthe thickness d of the modified portion 102 is to be made, the largerthe costs required for the modification treatment.

From these points of view, it is desirable that the thickness d of themodified portion 102 be set in the range of 1 nm to 1 μm, and morepreferably 2 nm to 100 nm.

Other than changing the time length for the exposure to the activatedgas 20, the thickness d of the modified portion 102 can be also adjustedby changing constituents of the source gas 14 (a ratio between the inertgas and the reactive gas) as well as by changing voltage and frequencyof the high-frequency electric field. For instance, the thickness d ofthe modified portion 102 increases as the ratio of the reactive gas inthe source gas 14 is raised.

Accordingly, the thickness d of the modified portion 102 can be adjustedto be in the desirable range by incorporating these parameters.

The phosphor particles 100 each having the modified portion 102 may bedistributed to the entire phosphor layer 23, from the surface to theinside. However, it is mainly the surface region of the phosphor layer23 that, in fact, is excited to thereby emit light when ultravioletlight is radiated to the phosphor layer 23 from the surface side, andnot much excitation-emission is produced from the inside of the phosphorlayer 23. Accordingly, only the surface of the phosphor layer 23 and thevicinity may be exposed to the activated gas 20 so as todisproportionally distribute the phosphor particles 100 having amodified portion 102, namely, to distribute more to the surface of thephosphor layer 23 and the vicinity than to the inside. In this casealso, the effect of suppressing the time-lapse deterioration in thephosphor layer 23 can be fully achieved.

1.4 Preferred Configurations in Modification Treatment

It is thought that the condition in which the source gas 14 is excitedwill be changed according to parameters such as a type of gas used, agas flow volume, a gas temperature, and a frequency and an intensity ofthe applied high-frequency electric field. Here, in order to achieve themodification effect of the phosphor particles, it is desirable thatthese parameters be adjusted so as to bring the activated gas 20 to aplasma state. This is because, since the reactive gas can be maintainedin an excited state once the activated gas 20 has been brought into aplasma state, the reactive gas is applied to the surface of the phosphoras remaining in an excited state.

Regarding high-frequency power applied by the high-frequency powersource 21, it is preferable that the voltage be set in the range of 10 Vto 10000 V while the frequency be set in the range of several kilohertz(kHz) to several tens of gigahertz (GHz).

As described above, it is desirable to mix inert gas, such as Ar, forexample, in the source gas 14 in order to reduce plasma damage exertedon the phosphor particles 100. Note however that, when the electronmobility of the reactive gas is lower than that of the rare gas (He)used for an electric discharge, the plasma damage to the phosphorparticles 100 can be reduced to a minor degree without inert gas such asAr being mixed in.

A location at which high-frequency power is applied to the source gas 14is preferably separated from a location at which the phosphor is exposedto the activated gas 20 in order to reduce the plasma damage to thephosphor particles 100. In view of this matter, the phosphor treatmentapparatus above has a structure in which high-frequency power is appliedto the source gas 14 within the reactor vessel 17 while the phosphor isexposed to the activated gas 20 outside the reactor vessel 17.Therefore, the high-frequency voltage will not directly applied to thephosphor, and the phosphor will not be exposed to the plasma dischargespace. Thus, this structure allows to reduce the plasma damage to aminor degree.

As a method of exposing the phosphor layer 23 to the activated gas 20,an atmosphere of the activated gas 20 may be formed sufficiently largeto cover the entire processing object 22. However, when the processingobject 22 has a large area to be processed, the atmosphere of theactivated gas 20 has to be formed substantially large. Furthermore,realizing this requires additional time.

On the other hand, with the above phosphor treatment apparatus, theactivated gas 20 ejected from the outlet 19 is sequentially applied topart of the phosphor layer 23 so as to scan through the phosphor layer23 along the surface. By the use of this method, even when the phosphorlayer 23 to be processed has a large area, there is no need to form theatmosphere of the activated gas 20 over an extensive area.

In addition, since the time length for the exposure to the activated gas20 can be adjusted for each part of the phosphor layer 23, uniformprocessing can be accomplished over the entire phosphor layer 23.

Furthermore, the thickness d of the modified portion 102 in the phosphorparticles 100 (i.e. how deep to be modified from the surface of theparticles) can be adjusted by changing the scanning speed or the numberof scans.

1.5 Matters Related to Modification of Phosphor Layers Used for DisplayDevices

Here are described matters related to the case of modifying phosphorlayers used for image display devices, and light-emitting elements likea lamp.

With a color image display device like a PDP, several different types ofphosphor layers are formed on a substrate, usually with three (red,blue, and green) or more phosphor layers separated from one another. Inthe PDP illustrated in FIG. 9 also, the color phosphor layers 9-11 (red,green, and blue), each of which is composed of an oxide phosphor, arearranged in a stripe pattern. In general, BAM phosphor, Zn₂SiO₄:Mn, and(Y_(x)Gd_(1-x))BO₃:Eu are used as a blue phosphor, a green phosphor, anda red phosphor, respectively.

It is sometimes the case that each color phosphor has its own kind ofdeterioration factors. In such a case, the modification treatment may beconducted individually for phosphor layers of each color formed on thesubstrate.

Among the blue, green, and red phosphor layers, the above treatment maybe used only for the blue phosphor layer which is comparativelyvulnerable to deterioration over time.

In addition, the blue and green phosphors, out of the three used for aPDP, tend to deteriorate by moisture. However, with the blue phosphor,deterioration due to the moisture adsorption can be suppressed byreducing the crystal defects. Accordingly, for the blue phosphor layer,an oxidation treatment may be performed on the surface of the phosphorparticles using source gas including oxygen as the reactive gas. On theother hand, for the green phosphor layer, a fluoride treatment may beperformed on the surface of the phosphor particles using source gasincluding fluorine as the reactive gas to give water repellency.

When the modification treatment is conducted, using the above phosphortreatment apparatus, individually for the phosphor layers of each colorformed on the substrate, the activated gas 20 can be applied only to thephosphor layers of a particular color by forming a tip of the outlet 19of the reactor vessel 17 into a narrow tubular structure.

As shown in FIG. 3, when the red, green, and blue phosphor layers 9-11are arranged in a repeating stripe pattern, the activated gas 20 can beapplied to a plurality of phosphor layers of the same color (threephosphor layers 9 of blue, in an example shown in FIG. 3) simultaneouslyby branching the tip of the outlet 19 to form a comb-like structure inaccordance with the interval of the phosphor layers of a particularcolor.

In phosphor layers of a display device, vulnerability to the time-lapsedeterioration differs depending on location, with some locations moreprone to be affected than others. Therefore, such vulnerable locationswithin the phosphor layers are exposed to the activated gas 20 for alonger time period so as to increase the thickness d of the modifiedportion 102 formed in the phosphor particles.

In the case of a PDP, for example, phosphor layers in a peripheralregion of the panel are more susceptible to deterioration as compared tothe central region. Accordingly, when the activated gas 20 is applied tothe phosphor layers, the length of the exposure time may be set longerfor the peripheral region than for the central region, so as to increasethe thickness d of the modified portion 102 of the phosphor particles100 in the peripheral region.

A fluorescent lamp used for a luminaire, on the other hand, has astructure in which a substance that emits ultraviolet light with anelectric discharge is filled in a glass tube where a phosphor layer isformed on the inner surface. In many lamps of this kind, mercury isfilled in the glass tube. However, regarding a mercury-free fluorescentlamp, Xe gas is filled instead, and the phosphor layer is excited byvacuum ultraviolet light emitted from the filled gas to thereby emitvisible light.

The above treatment method may be applied to such a glass tube having aphosphor layer formed therein so as to modify the phosphor layer, andthereby produce a lamp having little changes over time.

Regarding a three-wavelength fluorescent lamp, a phosphor layer isformed with at least a red, green, and blue phosphor in the mixtureform.

Also in such a case where several different types of phosphors are mixedin a phosphor layer, each type may have it own kind of deteriorationfactors. Here, the modification treatment may be repeated so as toeliminate deterioration factors unique to respective phosphors. Forexample, the treatment aimed at the blue phosphor described above isperformed using source gas including oxygen as the reactive gas, and thetreatment aimed at the green phosphor is carried out using source gasincluding fluorine as the reactive gas.

1.6 Matters Related to Modification of BAM Phosphor

The present invention is effective for oxide phosphors, and particularlyso for oxide phosphors using manganese ions or rare-earth ions as theluminescent center.

These types of phosphors are widely used in PDPs and three-wavelengthfluorescent lamps because they achieve high luminous efficiency.However, oxygen vacancies are readily formed in the phosphors, whichleads to degradation of luminance. Especially BAM used as a bluephosphor is susceptible to deterioration over time. Accordingly, anexceptionally profound effect can be obtained by performing themodification treatment on the surface of these types of phosphors.

The following gives details of the case where the modification treatmentof the present invention is performed on BAM phosphor.

In general, BAM phosphor is expressed as Ba_(1-x)Sr_(y)Eu_(z)MgAl₁₀O₁₇,where 0.05≦x≦0.40, 0≦y≦0.25, 0.05≦z≦0.30, and x−y≦z, with europium (Eu)metal functioning as the luminescent center.

Although BAM phosphor exhibits good luminescent characteristics as ablue phosphor, a great number of crystal defects are present in crystalsof BAM phosphor, and these crystal defects is a factor leading tochanges in chromaticity and luminance.

In addition, BAM phosphor is subject to changes, especially, inchromaticity cased by moisture, and here, degradation of luminance isalso accelerated.

Therefore, the problem of using BAM phosphor for phosphor layers of aPDP and a fluorescent lamp is that changes in chromaticity along withthe degradation of luminance are readily caused by BAM phosphor comingin contact with moisture during the manufacturing process.

By performing the above modification treatment on such BAM phosphor,crystal defects formed on the surface of BAM particles are compensated.In particular, the crystallinity is improved by the modificationtreatment using source gas including oxygen as the reactive gas.Herewith, BAM phosphor having smaller changes in chromaticity and lessluminance degradation can be realized.

In BAM phosphor thus modified, divalent europium and trivalent europiumare mixed. Here, if the phosphor particles are observed at an individualparticle level, a proportion of divalent europium to the total amount ofeuropium (i.e. a sum total of divalent and trivalent europium) withinthe entire particle is desirably no less than 60% and no more than 95%.As to the vicinity-included surface region within each of the particles,however, it is desirable that the proportion of divalent europium be noless than 5% but no more than 30%, and more preferably no less than 10%but no more than 20%.

Furthermore, when source gas including fluorine atoms is used,chromaticity changes and luminance degradation of BAM phosphor can besuppressed since moisture adsorption to BAM phosphor is reduced.

1.7 Experiment

BAM phosphor was applied onto quartz substrates to form phosphor layers,and the modification treatment was repeated on these phosphor layers.Here, mixed gas formed by adding He and Ar to oxygen functioning asreactive gas was used as the source gas for the treatment.

Respective testing samples were prepared by performing the treatment onthe phosphor layers either 0, 5, 10, 15, or 20 times.

A deterioration test was carried out in a high-temperature andhumidified atmosphere so that the prepared testing samples were exposedto a humidified atmosphere of approximately 450° C. with the use of atubular duct. Chromaticity y prior to and after the deterioration testwas measured.

“Chromaticity y” is a y-value on an x-y chromaticity coordinate planewhich represents a two-dimensional color space according to the CIEstandard calorimetric system.

As a blue phosphor deteriorates, the y-value largely changes while thex-value shows small changes, and therefore the y-value was used as theassessment criterion.

FIG. 4 is a characteristic graph showing the results of the experiment.The results indicate that deterioration in chromaticity y of thephosphor can be suppressed by performing the modification treatment onthe phosphor. In addition, it can be also seen that, as the number oftreatments performed increases, deterioration in chromaticity y becomessmaller.

1.8 Alternatives

The following gives an account of other equivalent ways of achieving thephosphor treatment apparatus and the treatment method of the firstembodiment.

(1) The above treatment method exemplifies the case where the phosphorlayers 23 formed on the substrate 22 a were processed, however thetreatment may be performed on phosphor particles in a powder forminstead. For example, a bulk of phosphor particles may be placed in atray, and set on the stage 24 for the treatment.

(2) In the above treatment method, the stage 24 carrying the processingobject 22 is set in motion so that the outlet 19 scans the surface ofthe phosphor layers. However, instead of moving the stage 24, the outlet19 of the reactor vessel 17 may be moved, or both the stage 24 and theoutlet 19 can be set in motion.

(3) Reactive gas, rare gas, and inert gas, which compose the source gas14, do not have to be in a gaseous form at ambient temperatures, andthey may be liquid or solid as long as they can be converted to agaseous form.

In order to obtain source gas in which the reactive gas and inert gasare mixed together, for instance, inert gas is bubbled and poured into aliquid where reactive gas (e.g. oxygen, halogen, halide, and fluorinatedgas) has been dissolved.

(4) In the above treatment method, the phosphor treatment apparatus isused to expose the phosphor layers 23 of the processing object 22 to theactivated gas 20 in order to modify the phosphor layers 23.Alternatively, however, by applying a liquid, in which reactive gas(e.g. oxygen, halogen, halide, and fluorinated gas) has been dissolved,to the surface of the phosphor layers 23, the vicinity-included surfaceregion of the respective phosphor particles 100 in the phosphor layers23 can be modified.

2. Second Embodiment

As in the first embodiment above, the second embodiment also modifiesthe vicinity-included surface region of phosphor particles by applyingenergy to raise the introduced source gas to an excited state andthereby generate activated gas, and exposing phosphor to this activatedgas.

Note however that, while a high-frequency power is applied in the firstembodiment in order to excite the source gas, in the second embodimentultraviolet (UV) light is radiated to the source gas instead.

2.1 Structure of Phosphor Treatment Apparatus

FIG. 5 shows a structure of a phosphor treatment apparatus used in thesecond embodiment.

A reactor vessel 31 where the source gas is to be introduced and excitedis provided in the phosphor treatment apparatus.

Provided with this reactor vessel 31 are an oxygen inlet 32 forintroducing oxygen gas as source gas, a nitrogen inlet 33 forintroducing nitrogen gas, and an outlet 34 for discharging gas afterbeing used.

Additionally, in the reactor vessel 31, a stage 37 for placing thereon aprocessing object 35, and a UV lamp 39 for emitting UV light 38 to theintroduced source gas are installed.

The stage 37 can be heated to a predetermined temperature by atemperature controller 40. The UV lamp 39 is a Xe excimer lamp, forexample, and is driven and controlled by a UV lamp controller 41.

The processing object 35 is composed, in the same manner as theprocessing object 22 used in the first embodiment, by forming phosphorlayers 36 on a substrate.

2.2 Phosphor Treatment Method

A treatment method for processing the phosphor layers 36 with the use ofthe phosphor treatment apparatus above is described here.

After nitrogen gas is sufficiently supplied to the reactor vessel 31from the nitrogen inlet 33, the stage 37 is heated to a predeterminedtemperature (e.g. 300° C.) by the temperature controller 40. Once thepredetermined temperature has been reached, the supply of nitrogen gasis stopped, and then oxygen gas is introduced from the oxygen inlet 32.The oxygen gas is introduced at a rate of approximately 1 litter perminute (L/min), for instance, for 30 minutes after the temperature ofthe stage 37 is stabilized at the predetermined temperature. Theintroduced nitrogen gas and oxygen gas are discharged from the outlet34.

Then, after the oxygen gas has been fully distributed inside the reactorvessel 31, the UV lamp 39 is driven by the UV lamp controller 41 toirradiate the introduced oxygen gas with UV light. Herewith, the oxygengas is excited, and then activated gas including ozone (O₃) and oxygenatoms (O) is generated. Subsequently, the phosphor layer 36 is exposedto the activated gas, and the vicinity-included surface region of thephosphor particles is modified in the same manner as described in thefirst embodiment. The UV irradiation time is, for instance, 30 minutes.

Then, the introduction of the oxygen gas is stopped, nitrogen gas isintroduced into the reactor vessel 31, and the stage 37 is cooled toambient temperatures.

As described above, here a method, in which the oxygen gas is suppliedafter the temperature of the stage 37 has become constant, is adopted asa way of introducing the reactive gas. Herewith, a phosphor havingfavorable characteristics can be produced at a high yield over a shorttime period in a stable manner.

Note however that the oxygen gas may be supplied as the temperature ofthe stage 37 is being raised. The temperature is gradually increasedfrom a room temperature to a high temperature of approximately 300° C.to decelerate the reaction rate so that crystal defects formed on thesurface of the phosphor particles are filled. In addition, luminancedegradation due to oxidation of Eu can be mitigated.

Furthermore, the reaction rate may be reduced by introducing inert gas,such as nitrogen, together with the oxygen gas.

2.3 Structure of Modified Phosphor Particles and Advantageous Effects

The phosphor particles thus modified have the same characteristics asthe phosphor particles 100 described in the first embodiment above, andeach of the particles contains the unmodified portion 101 in theinternal region therein and the modified portion 102 in thevicinity-included surface region.

These phosphor particles bring about the same effect as the phosphorparticles 100. The crystallinity of the vicinity-included surface regionof the phosphor particles is improved, while carbon is excluded from thesurface of the phosphor particles and the surrounding. As a result, thetime-lapse changes in luminescent characteristics are suppressed ascompared to the phosphor particles with no modification treatmentperformed.

As described in the first embodiment, the phosphor particles can beapplied for modifying phosphor layers used for a luminaire (e.g. amercury-free fluorescent lamp) and for an image display device (e.g. aPDP).

When a PDP is to be produced, for example, phosphor layers of each colorare formed on the rear glass substrate, and then this rear glasssubstrate is placed on the stage 37 of the above phosphor treatmentapparatus to perform the modification treatment on the phosphor layers.Herewith, a PDP having small changes over time can be produced.

In the second embodiment also, the above treatment may be performed onlyon the blue phosphor layers among the blue, green, and red phosphorlayers formed on the rear glass substrate since the blue phosphor layersare comparatively susceptible to the time-lapse degradation.

2.4 Excitation of Oxygen Gas by UV Light

Here is given an account of a mechanism in which ozone and oxygen atomsare generated by irradiating oxygen gas with UV light.

When a light ray having a shorter wavelength in the UV range, called anozone producing radiation (1849 angstrom), is applied to oxygen (O₂)introduced to the reactor vessel 17, the molecular oxygen (O₂) is splitinto two oxygen atoms (O). Then, these oxygen atoms (O) combine withother molecular oxygen to form ozone (O₃).

When a light ray (2537 angstrom) which breaks ozone down is applied, theoxygen atoms (O) formed in the above decomposition reaction react withthe formed ozone (O₃), and break this down to further form monatomicoxygen.

In view of such a mechanism, if the UV lamp 39 is composed of a set oftwo different kinds of Xe excimer lamps aligned together, highlyreactive activated gas can be generated. Here, one kind of the Xeexcimer lamps emits radiation with a wavelength at which ozone isproduced (1849 angstrom), and the other emits radiation with awavelength at which ozone is broken down (2537 angstrom).

As this preferred embodiment, the introduced source gas can berelatively easily excited and activated by irradiating with UV light. Inaddition, the source gas can be excited while the treatment is performedat a low temperature, which allows a reduction in processing time aswell as cost savings.

In the above treatment method, when the phosphor layers 36 are exposedto the activated gas, the stage 37 is heated, and thereby the phosphorand the activated gas are brought to a heated state. This conditionaccelerates the modification treatment of the phosphor particles.

In the case where the UV lamp 39 is placed opposite the phosphor layers36 as in the phosphor treatment apparatus of FIG. 5 above, although theUV light 38 emitted from the UV lamp 39 is absorbed by the oxygen gas tosome extent, a portion of light reaches the surface of the phosphorlayers 36, and thereby the phosphor layers 36 deteriorate.

Accordingly, it is desirable that the phosphor layers 36 be not directlyirradiated with the UV light 38 emitted from the UV lamp 39.

For example, a shutter for blocking off the UV light 38 may be providedabove the processing object 35, and the shutter is closed only when theUV lamp 39 is in operation. Alternatively, a ceramic plate for blockingoff the UV light 38 may be placed with some space between the phosphorlayers 36 provided.

2.5 Experiment

Testing samples were produced by performing the modification treatmenton BAM phosphor by variously changing the heating temperature, asdescribed below.

The samples, in each of which phosphor layers were formed by applyingBAM phosphor onto a quartz substrate, were placed in a reactor vessel ofa commercially available ozone producer, and then the substrates wereheated. Nitrogen was supplied until the substrate reached apredetermined temperature, and then oxygen was supplied at a rate ofapproximately 1 L/min for 30 minutes after the temperature of thesubstrate was stabilized at the predetermined temperature. Thus, oxygenwas sufficiently spread in the reactor vessel, and then, UV light wasapplied for about 30 minutes to produce ozone. Subsequently, nitrogenwas introduced, replacing the oxygen, to cool down the inside of thereactor vessel.

Note that the temperature for heating the substrate was variouslychanged within the range up to 300° C.

Luminescence intensity of the testing samples was measured prior to andafter the modification treatment.

In addition, after the modification treatment was performed, thephosphor layers of individual testing samples were exposed to ahumidified atmosphere of approximately 450° C. with the use of a tubularduct. Thus, the phosphor layers were made to deteriorate at anaccelerating rate, and chromaticity y prior to and after thedeterioration test was measured.

FIG. 6 is a characteristic graph showing the results of the experiment,with chromaticity y prior to and after the deterioration test plottedaccording to the heating temperature.

In FIG. 6, the horizontal axis represents the heating temperature forthe modification treatment, while the vertical axis shows the measuredchromaticity y. The dash line and solid line in the figure denotechromaticity y prior to and after the deterioration test, respectively.

As the treatment was performed at a higher temperature, the chromaticityy measured after the deterioration test became lower. As to the samplesprocessed at a heating temperature of 300° C., chromaticity y measuredprior to and after the deterioration test remained almost unchanged, andthese measured values are similar to the initial value (i.e.chromaticity y measured with no deterioration test performed).

What this means is that deterioration in chromaticity y of the phosphorbecomes less when the modification treatment is performed at a higherheating temperature. This is thought to be attributable to the reactionat the vicinity-included surface region of the phosphor particlesaccelerates as the heating temperature is increased, and oxygenvacancies around the phosphor surface are filled over a short period oftime.

FIG. 7 is a characteristic graph showing luminescence intensity measuredafter the modification treatment, and plotting the luminescenceintensity according to the heating temperature. The horizontal axisrepresents the heating temperature for the treatment, while the verticalaxis shows the luminescence intensity ratio. This luminescence intensityratio is a proportion of the luminance of the phosphor measured afterthe modification treatment in relation to the luminance of theunprocessed phosphor in an initial condition.

The results shown in FIG. 7 indicate that, as the treatment wasperformed at a higher temperature, the luminescence intensity measuredafter the treatment became lower. It is considered that this is becausethe oxidation of Eu metal functioning as the luminescent centeraccelerates as the heating temperature is increased. On the other hand,little reduction in the luminescence intensity as a result of thetreatment can be seen when the treatment is performed at a lower heatingtemperature, and, in particular, at 100° C. or lower.

According to the above experimental results, a phosphor having smallchanges in chromaticity y over time can be realized by: setting theheating temperature for the treatment low; reducing the reaction rate sothat monatomic oxygen is distributed, within each of the phosphorparticles, only to a shallow region from the surface; and lengtheningthe processing time of the treatment (e.g. processing at 100° C. for sixhours) so as to prevent oxidation of Eu and thereby maintain theluminance of the phosphor.

Note that, even if the heating temperature is set as high as 300° C., byreducing the processing time to 30 minutes or less, a phosphor havingsmall changes in chromaticity y can be formed while a reduction in theluminescence intensity is suppressed.

3. Third Embodiment

The third embodiment is identical to the second embodiment above, butdiffers in the use of gas including fluorine atoms as reactive gas, inaddition to oxygen gas.

FIG. 8 shows a diagrammatic drawing of a phosphor treatment apparatusaccording to the third embodiment.

Although having a similar structure as the phosphor treatment apparatusshown in FIG. 5 above, this phosphor treatment apparatus has a reactorvessel 31 in which a fluorinated gas inlet 42 is provided as asource-gas inlet in addition to the oxygen inlet 32 and the nitrogeninlet 33.

The following describes how to process the phosphor layers 36 of theprocessing object 35 using the above phosphor treatment apparatus.

After nitrogen gas is sufficiently supplied to the reactor vessel 31from the nitrogen inlet 33, the stage 37 is heated to a predeterminedtemperature (e.g. 150° C.) by the temperature controller 40. Once thepredetermined temperature has been reached, the supply of nitrogen gasis stopped, and then fluorinated gas is introduced from the fluorinatedgas inlet 42 at the same time as oxygen gas is introduced from theoxygen inlet 32. Thus, mixed gas composed of oxygen and fluorinated gasis introduced to the reactor vessel 17.

Specific examples of fluorinated gas are CF₄, SF₆, CHF₃, and NF₆.

When CF₄ is used as the fluorinated gas here, the flow volume ratio ofoxygen gas and CF₄ should be around 1 to 1.

Once the oxygen gas and fluorinated gas have been fully distributedinside the reactor vessel 31, the UV lamp 39 is driven by the UV lampcontroller 41 to irradiate the introduced oxygen gas and fluorinated gaswith UV light. Herewith, the oxygen gas is excited to form ozone (O₃)and oxygen atoms (O). Concurrently, the fluorinated gas is excited toform fluorine atoms (F).

As a result, activated gas including ozone (O₃), oxygen atoms (O), andfluorine atoms (F) is generated, and the phosphor layers 36 are exposedto the activated gas. Herewith, crystal defects in the vicinity-includedsurface region of the phosphor particles are compensated in the samemanner as described in the second embodiment. On top of this, thefluorine atoms react with the vicinity-included surface region of thephosphor particles to form a water repellent layer on the surface of thephosphor particles.

Then, the introduction of the oxygen and fluorinated gases is stopped,nitrogen gas is introduced into the reactor vessel 31, and the stage iscooled to ambient temperatures.

The phosphor particles processed with the treatment method according tothe third embodiment can achieve improved crystallinity of thevicinity-included surface region. Furthermore, moisture adsorption tothe phosphor is reduced, which in turn leads to suppressing thetime-lapse changes in the phosphor due to the moisture adsorption.

As well as ozone and monatomic oxygen, fluorine atoms also have aneffect of eliminating impurities present in the vicinity-includedsurface region of the phosphor particles.

Of course, it is not to be argued that the treatment method of the thirdembodiment can also be applied for modifying phosphor layers for aluminaire (e.g. a mercury-free fluorescent lamp) and for an imagedisplay device (e.g. a PDP).

INDUSTRIAL APPLICABILITY

Thus described above, since being capable of suppressing time-lapsechanges in phosphor layers, the present invention can be applied formanufacturing a longer lasting luminaire and PDP.

1. In a plasma display panel having a light-emitting element, theimprovement comprising: an oxide phosphor in particulate form, whereineach particle has a surface region including a vicinity thereof modifiedso that an elemental composition of the surface region includes morehalogen than an elemental composition of an internal region of theparticle.
 2. The plasma display panel of claim 1, wherein halogen atomsare chemically bound to the surface region.
 3. The plasma display panelof claim 2, wherein fluorine atoms are chemically bound to the surfaceregion.
 4. The plasma display panel of claim 1 having one or morephosphor layers containing the oxide phosphor.
 5. The plasma displaypanel of claim 1 wherein the phosphor particle in an alkaline earthmetal aluminate phosphor.
 6. The plasma display panel of claim 5 whereinfluorine is bonded with the alkaline earth metal aluminate phosphorparticles.
 7. The plasma display panel of claim 1 wherein the phosphorparticles are Europium-activated oxide phosphors.
 8. In a plasma displaypanel having a light-emitting element, the improvement comprising: aphosphor layer for suppressing time-lapse changes in luminescentcharacteristics of the light-emitting element including oxide phosphorparticles having surface regions of the particles modified so that anelement composition of the surface region includes more of halogen thanan elemental composition of an internal region of the particles.
 9. Aplasma display panel including one or more phosphor layers eachcontaining an oxide phosphor in particulate form, wherein an oxidephosphor in which each particle has a surface region including avicinity thereof modified so that an elemental composition of thesurface region includes more halogen, than an elemental composition ofan internal region of the particle, the halogen is disproportionallydistributed, with more residing at and near a surface of the phosphorlayers than in an inner region of each of the phosphor layers.